Male and female intact and castrated rhesus monkeys and guinea pigs will be utilized to determine pituitary sensitivity to luteinizing hormone releasing hormone and hypothalamic-pituitary sensitivity to negative feedback effects of gonadal steroids during the period of and the period following the neonatal elevation of testosterone secretion found in the male. The bioavailability of circulating androgens secreted in male rhesus during the neonatal period will be contrasted with that of the adult by assessing gonadal steriod binding proteins. Steroidogenic capabilities of male and female gonads and their relative sensitivity to gonadotropin stimulation during and following early neonatal development will also be determined. Localization of brain cellular distribution of luteinizing hormone releasing hormone will be performed by use of immunocytochemical techniques in neonatal animals during and following the period of increased testicular steroidogenesis. Studies of the development of pituitary receptors for luteinizing hormone releasing hormone will also be performed.